This valve for controlling the flow of high pressure working fluid is suitable for use on well heads used in offshore oil drilling installations and other uses. The valve has an actuator which is preferably a cylinder-and-piston motor and it has a spring for moving the valve element in one direction, the cylinder-and-piston motor serving to move the valve element in the other direction.
There is an intermediate chamber, to which sea water has access, between the actuator and the valve chamber. Although the spring can be made of stainless steel, such material after being tempered to form a spring is subject to deterioration when exposed to sea water. It is a feature of the present invention that the sea water chamber is sealed off from the space that houses the spring. This space is preferably at the same pressure as that used to operate the cylinderand-piston motor, and in the preferred construction, a pilot valve that supplies working fluid to the cylinder and piston motor is operated with its minimum pressure at least as high as the pressure in the sea water chamber so that if any leakage occurs at the seal, the leakage will be toward the sea water chamber.
Another feature of the invention is that the piston which operates the valve element, has a piston rod which extends from the actuator through the sea water chamber to the valve chamber; and the piston and piston rod assembly which is a rigid unitary structure, is guided in spaced-apart guide bearings at opposite sides of the sea water chamber.
A shoulder, which is a rigid part of the piston structure, is used to compress the spring against a fixed part of the housing.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.